A small power boat, perhaps in the 40 foot size, only carries enough fuel to get you a few hundred miles. So now you are 400 or 500 miles offshore and run out of gas. What to do next? Do not take a power boat. Get yourself a sailboat. Just how big should it be. The space between the crests of the ocean waves dictates that you should have about 35 feet or more at the waterline, accordingly, you will need a vessel of 40 feet or more.